1. Field of the Invention
The present invention relates to a cooling fan apparatus for an automobile, especially to a cooling fan, a fan shroud and a protecting screen for a cooling fan, which are located in front of a radiator in the engine compartment of an automobile.
2. Background Information
A cooling fan is disposed in front of a radiator, which is used to cool engine coolant, and a condenser, which is used to condense refrigerant of an air conditioner.
FIG. 12 shows a conventional cooling fan apparatus. A cooling fan 2 is located in front of the condenser 1 where the left of the Figure is closest to the front of the automobile. The cooling fan has a boss 3 at the center of the fan, wherein an electric motor 4 is disposed. A fan shroud 5 is disposed around the cooling fan 2. A screen 6 is connected to the fan shroud 5 at a front end thereof. A bracket 7, which is formed integrally with the fan shroud 5, is disposed at a center portion of the screen 6. The electric motor 4 has a hub 8 which is connected to the bracket 7 through a rivet 9, so that the electric motor 4 is fixed on the center axis of the protecting screen 6.
As shown in FIG. 13, the screen 6 has a plurality of rings 10 which are disposed concentrically from an outer periphery to an inner periphery of the protecting screen 6.
An object of this invention is to reduce the noise and increase the cooling efficiency of the operating fan.
During research it was noticed that turbulence of air flow through the fan shroud 5, is one cause of fan noise. The air turbulence around the screen increases when the automobile is stopped, namely when the engine is idling, because the cooling fan forcefully draws air into the engine compartment. As shown in FIG. 15, an early improvement was to make a clearance X between the fan shroud 5 and the screen 6 in order to smooth the air flow. The noise level was reduced 0.5 dB.
According to the result of the improvement described above, the inventors disposed a bell mouth ring 11 at the outer periphery of the screen 6, as shown in FIG. 16, in order to further smooth the air flow which flows through the clearance X. The noise of the cooling fan 2 shown in FIG. 16 is 0.9 dB less than that of the cooling fan 2 shown in FIG. 15 In addition, the amount of air flowing through the cooling fan 2 shown in FIG. 16 is increased by about 5% over that of cooling fan 2 shown in FIG. 15. Additional improvements are also possible.
Air turbulence over the rings of the screen can be reduced. The cooling fan shown in FIG. 13 has protective rings 10 up to the outer periphery of the screen. The air turbulence resulting from the rings is significant especially in the vicinity of the outer periphery of the screen 6. As shown in FIG. 17, the air flow is disturbed behind ring 10a and ring 10b which are disposed at the outer periphery of the screen 6. In order to reduce such air turbulence, a radial grid 12 is disposed at the peripheral portion of the screen 6 as shown in FIG. 18, reducing the noise level by 0.6 dB as compared with the cooling fan 2 shown in FIG. 16.